Remote controlled recording machine



April 3, 1951 R. KOBLER REMOTE CONTROLLED RECORDING MACHINE 2Sheets-Sheet 1 Filed Oct. 8, 1946 BYQ Patented Apr. 3, 1951 umrso REMOTECONTROLLED RECORDING MACHINE Richard Kobler, San Francisco, Calif.

Application October 8, 1946, Serial N 0. 701,896

The present invention relates to systems adapted to permit use of arecording machine from a remote station, and more particularly itrelates to electrical circuit arrangements enabling operation of anelectronic'recording machine from a plurality of remote stations.

In the past it has been necessary in systems of this type to connect therecording machine with every remote control station through a pluralityof difiierent lines, each serving a distinct function of its own. Thus,such systems required (1) a shielded line for each remote controlstation to feed the audio input to the recording machine, (2) a powerline for starting and stopp ng the motor of the recording instrument,(3) an additional power line to activate or interrupt warning lightsprovided at all of the stations for the purpose of indicating theavailability of the machine, and (4) frequently also a third power lineto operate so-called stand-by lights at every one of the stations toindicate whether the machine (especially its electronic parts) wassufficiently heated to be in condition for use. It is self-evident thatthe necessity of having so many power lines in addition to a shieldedaudio line between the recording machine and every one of the remotestations rendered such systems complicated, costly, and difiicult toinstall. This is especially true for the power lines which have to beplaced into B-X cables if they exceed 8 or 10 feet in length to satisfyfire prevention and building regulationsin most towns and cit es, to saynothing of the fact that the installation of such cables in addition tothose installed during construction is expressly forbidden in a greatnumber of modern ofiice buildings, and violation of any such rule mayvoid all fire insurance claims.

The audio lines provided in known remote control systems of the typeunder consideration offered seriousadditional problems. The pick-updevices generally used in these systems were either crystal orhigh-impedance dynamic microphones requirin high-impedance lines fortransmission. Such lines, however, are prone to pick up a considerableamount of hum and interferences fromv the adjoining power lines betweenthe remote station and the recording device, and indeed from any otherpower line in the buildingv as well as the usual sources of radiointerference. It was impossible, therefore, to include the audio linesin the same cable as the power lines; in fact, they had to be enclosedin special shields and had'to be conducted at random or placed amaterial distance apart from power lines. All these factors addedmaterially to the cost of the known remote control systems and their Iinstallation without entirely eliminating disturbances in the audiolines; therefore-in spite ofall precautions the effective range ofoperation of-these known remote control arrangements was severelylimited,

12 Claims. (01. 17 96) because beyond a certain point the speech-tonoiseratio became too unfavorable for intelligible recording. To make mattersworse, this disadvantage was still more accentuated by the necessity ofemploying powerful amplifiers in the recording machine due to the Weakout-put levels of the crystal or high-impedance dynamic microphones andthe enormous line losses inherent in high-impedance lines, because theamplifiers did or other'interference.

not only amplify the sound output of the remote microphones but also theinterferences picked up by the high-impedance line.

Thus, in spite of their very obvious value in business establishments,hospitals, government administration buildings, etc., remote controlledrecording machines have not become popular because, (1) they were tooexpensive, (2) their installation was too costly and too complicated andfrequently disfigured walls and ran counter to fire preventionregulations, (3) their rangepf operation was limited, and (4) thequality of the recordings obtained was not dependable and mostlyunsatisfactory.

Broadly, it is an object of the present invention to provide a circuitarrangement for the operation of a recording machine from a number ofremote stations, which is inexpensive and easy to install and operate.

It is another object of the present invention to provide a circuitarrangement of the type referred to, wherein the interconnecting linesconstitute no fire hazard and comply in all respect with thecontemporary building and insurance regulations.

'More specifically, it is an object of the present invention toeliminate the conventional use of 110 volt power lines between remotestations and the recording machine in systems of the types referred towhile retaining the remote control functions previously performed'bythese lines. 7

It is an additional object of the present invention to furnish a circuitarrangement adapted to permit operation of a recording device from anumber of remote stations wherein the recording device requires only lowamplification of the audio signals arriving from the remote stations.

' It is yet another object of the present invention I to provide acircuit arrangement enabling operation of a recording machine over thelargest practicable distances in systems of the type under discussion,without harmful deterioration in the recording qualitydue to theintroduction of hums At'the same time it is another specific object ofthe present invention to achieve these results without requiring specialshielding for the audio lines.

.. It is a specificobject of the present invention to-provide a circuitarrangement of the type restations, wherein transmission of the audiosignal from a remote station to the recording device and control ofrecording machine and warning lights are efiected through a single lowvoltage, low-impedance line.

It is also an object of the present invention to provide each remotestation in systems of the type referred to, with a warning signaladapted to' in dicate engagement of the recording machine by anotherstation whether the motor of the machine is running or not. Moreover, itis an object of my invention to so arrange this warning signal that itwill act as a stand-by light as Well as a busy signal indicating notonly availability but also readiness of the recording machine.

Lastly, it is an object of this invention to adapt the remote stationsof my novel system to the reception for recording purposes,- oftelephone messages by operation of a simple switchand with the highestdegree of safety against shortcircuits of either the D. C. or the audiocom ponent of the telephone line.

These and other objects of the present invention will be apparent fromthe following olescription of the accompanying drawing which illustratescertain preferred embodiments thereof and wherein:

Figure 1 is a circuit diagram representative of an electronic recordingdevice and two remote stations;

Figure 2 is the circuit diagram of a. remote control station having amodified busy signal system;

Figure 3 is the circuit diagram of a remote control station having yetanother busy signal system; and

Figure 4 is the circuit diagram of two remote control stations ofsimplified design.

In Figure 1 block A drawn in broken lines indicates the electronicrecording machine; block B indicates the master control station which isusually in close proximity of the recording machine; and blocks C and Dsignify remote control stations.

The electronic recording machine A includes an amplifier It representedby a block drawn in full lines. Amplifier H) feeds amplified audiosignals to the recording head II which may, for instance, be of thecrystal type. An electric motor 12 is provided to drive the mandrel 12aof the recording instrument. Power from a suitable source such as a 110volt light line is drawn at l3 which denotes a plug contact of theconventional type. switch 1 A is provided to permit convenientactivation of the arrangement. When switch I4 is closed, power from theline is supplied through leads i5 and it directly to amplifier Ill towarm up its filaments (heaters and possibly plate power supplies) andprepare the amplifier for immediate use. At the same time power issupplied through leads l8 and [9 to the primary winding 2! of astep-down transformer 28 situated in master control station B thesecondary winding 22 of which is connected across a selenium rectifier23 of suitab e design. Thus the high voltage A. o. supplied from theline is stepped down in transformer 29 and appears as a pulsating 'D. C.

of materially lower voltage across output leads I 24 and 25 of seleniumrectifier '23. A suitable filter system for instance in the form of achoke coil 26 and condensers 28 and 29 connected across leads 2G and 25at either end of choke coil 26 serves to even out the pulsations of thelecti'fi'er A master control or stand-by output so as to provide asteady low voltage D. C. suitable for the transmission of telephonicmessages originating in resistance type microphones.

While one side of the power line I9 is per manently connected to themotor through lead it and branch it, the closing of master switch 54brings up the other side of the line to the motor through a branch I8 oflead 18 over a normally open switch 46 which may be closed by theoperation of a relay 60 under conditions to be described hereinafter.

Likewise, while one side of the power line It is permanently connectedto the primary winding 5% of a step-down transformer 58 through a branch[9, the closing of master switch It brings up the other side of thepower supply line to the primary winding 51 through lead is, a portionof branch I8 and a secondary branch it" over a normally open switch itwhich may be closed by a relay 65 under conditions to be describedhereinafter. Step-down transformer 58 has a secondary 52 adapted tosupply the transformed A. C. voltage through leads 53 and 54 to sourcesof light 5% and 58 located in remote control stations C and D,respectively. It will be understood that lights 56 and as may also besupplied with a D. 0. current, for instance, by appropriate employmentof a selenium rectifier.

Reverting to the output circuit of selenium rectifier 23, connected inseries with choke coil 26 are two relays t0 and 65 arranged in serieswith one another and as previously mentioned adapted to close switchesand respectively. Relays 65 and 65 are designed to be of difierentsensitivity, relay 5!] requiring a greater current now in the D. C.circuit for operation of its armature than relay 65 for reasons whichwill presently appear.

It will be understood by those skilled in the art that the relays 60 andneed not necessarily be connected in series but may be ar rangedparallel to one another and may yet be made to successively operateswitches 45 and do as the current flow in the rectifier output sircuitincreases. It should be noted that aside from their purpose ofactivating switches 48 and 45 the relays 6t and 65 in conjunction withcondenser 38 form an additional stage of the previously mentionedfiltering system, which increases the evenness of the D. C. output ofrectifier 23.

The power supply system just described is part of the connecting circuitbetween remote stations C and D and master control station B. Thiscircuit includes a carbon microphone 38 in remote station C and theprimary 32 of an audio transformer 3| within the confines of mastercontrol station B the secondary 33 of said transformer 3| beingconnected across the input terminals of amplifier Ill. The connectingline between the remote control part and the master station part of thecircuit is formed by leads 35 and 36.

Within remote control station C, the circuit includes a resistor 39 anda selector switch 31. When switch 3! is closed in upward direction asviewed in Figure 1, it initiates a limited amount of current flow in theD. C. circuit provided stand-by switch I A has previously been closed.This current flow will be sufiicient to activate relay 65 which willclose switch 45 but will be insuifici'ent to operate relay 60 so thatswitch will remain open. When switch 45 is closed, the power supply linethrough primary 5i f stepdown transformer 50 will be i closed and as aresult thereof a low voltage A. C. .(or D. C.) will be supplied to lamp58 in remote station C and lamp 56 in remote station D, and, indeed, toall the corresponding lamps in whatever additional remote controlstations may be joined to the system of my invention. Thus, when 'apartycloses switch 31' in upward direction in remote control station C andlamp 56 in his station lights up, he will know that the standby switch14 was closed and that the machine is ready for use, while light 56' litup in control station D and any other associated remote station willwarn other parties intending to dictate through any of the other remotecontrol stations that the recording machine is engaged.

Current flow in the circuit initiated by the closing of switch 31,however, was not large enough, due to the presence of resistor 39, tocause operation of relay 6B for the purpose of closing switch 40, andmotor l2 therefore re'-.

mained at rest. 7

To enable an operator to start the motor as soon as he is ready todictate, means are provided to effectively eliminate resistor 39 fromthe circuit. For this purpose Wires Hi and II connected to either end ofresistor 39'lead to a switch 12 which is normally held open by suitablemeans, and maybe adapted to be closed by the operators foot. When theoperator steps on switch 12, wires Hi and H form a by-pass aroundresistor 39 and the resultant current increase in the D. C. circuit issunicient to cause relay Bl] to close switch 40; in consequence thereof,power is supplied to motor l2 and the recording cylinder [2a willcommence to revolve.

- If and when an operator wishes to interrupt there will be no waste ofrecording surface.

However, signal lights 56 in remote station C and the correspondinglights in any other remote stations that may be joined to my system,will remain illuminated, warning other prospective users that themachine is still engaged although the motor may not run at the moment.Only when the operator at remote station C has completed his work andreturns switch 31 to its neutral position, will lights 56 go out toindicate at all remote stations that the system is now available toother users.

The manner in which a voice dictating into the microphone of a remotecontrol station is transmitted to the recording device will be obviousto those skilled in the art from the foregoing description, but willbriefly be outlined in the following: The resistancechanges occurring incarbon microphone 38 in response to vocal vibrations will modulate thedirect current in the circuit imposing an alternating component upon theD. C. current flow. The resultant pulsating current will travel frommicrophone 38 through lead 35, to primary 32 of audio transformer 3|,with the alternating component returning through condenser 30, and lead36 back tomicrophone 38. High-impedance secondary 33 of audiotransformer 3| will respond to the alternatin'g component of thepulsating current passing through primary 32 and supply a corres'pond-'in'g'alternating potential to the input of ampliher It. Thus I am ableto control operation of the 'motorhoi the recording machine from theremote station by use of the same low impedance line which I employ fortransmission of audio messages and which constitutes no fire hazard anddoes not violate any fire prevention or insurance regulations.

Since the output level of a resistance type microphone, and especiallyof' a microphone of the carbon type, is relatively high, the alternatingvoice potential supplied by secondary 33 to amplifier II] will likewisebe relatively high so that itwill not be necessary to employ powerfuland expensive amplifiers inthe recording device to produce satisfactoryrecordings. Additionally, since the path travelled by the alternatingcomponent of the modulated D. 0. current is predominantly oflow-impedance, and the high-impedance path between secondary 33 and theinput of amplifier It] will usually be very short, very littleinterference will be picked up by the line, and the dictation suppliedto the amplifier will beremarkably free from hum or other disturbingnoises. Also there will be no practical limit as to the permissiblelength of the connecting line between remote station and inaster'stationsuch as exists in the known remote control systems employing highimpedance lines wherein the noise level will soon drown out thediminishing voice level as the length of the line in creases.

Aside from a position of rest and a position adapted to close the abovedescribed D. C. circuit through microphone 38 for the purpose ofdictation, switch 31 also has a third or downward position as shown inFigure 1 whereinit connects the secondary 82 of a transformer acrossmain leads 35 and 36 for the purpose of recording telephone messages.The primary 8| of transformer 80 is connected through attenuatingpotentiometer 83 across telephone tapping leads 81 and 88 each of whichcontains a blocking condenser and 86, respectively, to prevent the D. C.component of the telephone circuit from.

reaching the transformer 80. As an added safety againstaudio or D. C.short circuits over the protection afiorded by blocking condensers 85and 86, potentiometer 83, and transformer 89, I provide aresistor 84between primary winding BI and blocking condenser 85. The principalprotection, however, whichI secure in accordance with my invention forthe telephone net work, flows from the fact that'here no A. C. or

D. C. power lines are installed in the proximity of the audio lines aswas the case in the conventional remote control recording systems. Thus,the danger ever present in the known systems, of getting one or bothsides of the power line connected to the audio line is eliminated in itsentirety.

When a telephone message arriving at remote 'stationC is to be recorded,switch 37 is turned to connect secondary 82 of transformer 89 acrossleads 35 and 55, for which reason secondary 82 should be designed tohave approximately the same resistance as microphone 38. Secondary 8 2of transformer 80 now forms anintegral part of my low voltage D. C.control circuit in that its insertion closes said circuit and activatesrelays 60 and 65 and the switches 40 and 45 controlled by said relays,while elimination of secondary 62 from the circuit by operation ofswitch 3T-will stop the motor and extinguish the warning lights. Inthetelephone tapping circuit, condensers '85 and 86 while blocking theD. C. of the telephone line, permit the audio componenttlii'areof...tci-pa'ssthrough resistor =84 and potentiometer 33 to theprimary 8| of transformer 80 inducing corresponding potentials in thesecondary 82 thereof which are imposed upon the D. C. of thecommunication circuit and are transmitted to the amplifier II! of therecording machine over audio transformer 3! in master station B in themanner previously described.

It should be noted that since the communication circuit connectingremote station and master station is adapted to a carbon type microphoneas described above, no line balances will have to be incorporated in thesystem of my invention when used for the purpose of recording telephonemessages, because the output of a carbon microphone and that of atelephone tapping system of the type described are in close proximity,and whatever attenuation may be required when a remote control stationis set for the recording of a telephone message may be provided byregulation of potentiometer 84.

Any number of additional remote control stations may readily be joinedto my system as exemplified by remote control station D in Figure 1.Station D differs from station C merely in so far as it has no provisionfor the recording of telephone conversations but is otherwise identicalwith station C, and equivalent elements in remote station D havetherefore been identified by the same reference numerals as in station Cexcept that a prime has been added to the numerals in station D. As maybe seen from Figure 1, all that is necessary to join remote station D tothe system of the present invention, is to connect leads 35, 36', 53,and 54 of remote station D to the corresponding leads 35, 36, 53, and 54at any suitable points thereof, and the newly added remote station D maybe manipulated, and will operate, in exactly the same manner as stationC.

While each of the remote stations of my novel system is provided with awarning light 56 or 56', respectively, to indicate whether the recordingmachine is available or not, it may be desirable under certaincircumstances to have additional audible signalling means to warn aprospective user who may absentmindedly have overlooked lamp 56, that heis about to spoil another partys recording. For this purpose a suitablesound reproduction device 90 may be connected across leads 35 and 36 inshunt of microphone 38 and resistor 39 (or 35' and 35 in station D) asshown in Figure 1, a blocking condenser 9| (or 9| respectively) beingprovided in one of the leads to prevent direct current flow through theshunt line. Thus, when switch 31 is set to one of its operativepositions the voice of any party that may dictate into the recordingmachine through another remote control station such as station D willbecome immediately audible and warn the intended user that he overlookedbusy signal 56.

For this purpose I find it especially advantageous to use a combinedmicrophone and receiver of the type used in modern telephones, and I soarrange matters that lifting of the receiver from its rest for thepurpose of dictating into the recording machine automatically setsswitch 31 to operative position and activates light 56. Thus, when aperson lifts the receiver and places it to his head in the manner of anordinary telephone receiver, he will immediately hear the voice ofwhatever party may at the time dictate into the machine, and willtherefore refrain from using the machine.

In Figure l I have shown the warning lamps 56 in the remote controlstations as operated by a transformed A. C. current drawn from the mainpower line at I3 and supplied to the remote stations through a step-downtransformer 50 situated in the master station and over low voltage lines53, 54 and 53', 54, respectively. It may be preferable, however, if thenumber of control stations is considerable, to modify the warning lightsystem to the form shown in Figure 2, wherein like numerals are used toidentify parts analogous in form and function with parts shown inFigure 1. A relay me is substituted for the incandescent warning light56, and said relay is adapted to actuate a normally open switch I02 toclose a circuit IIlI including a neon lamp I03 and a local source ofpower 1M which may be a conventional power supply of 110 volts. By usingthis modified warning light system, the number of control stations canbe greatly expanded without consuming any more current in the variousrelays I than is ordinarily consumed by about five warning lights 56 ofthe incandescent type shown in Figure 1.

Figure 3 shows another modification of the warning light system. In thisparticular embodiment the flow of D. C. current in the communicationcircuit initiated by the closing of switch 3'! is arranged to operate arelay I I0 provided in the circuit within the confines of the remotecontrol station. When relay III] is excited, it closes a normally openswitch I I I to complete a circuit H2 drawing power from a local sourceof power H3 which may again be a conventional power line of volts. Astep-down transformer IIA having its primary H5 in circuit H2, suppliesa low voltage A. C. through secondary I5 to an incandescent type lam111. Thus, lamp II! will light up as soon as current flows in the D. C.circuit upon closing of switch 3?. In a remote control system employinga warning light arrangement of this type, master control station andremote stations will in fact be connected by only a single low voltageD. 0. line 35, 35, plus ground.

Other variations Of my warning light system will readily occur to thoseskilled in the art once they have familiarized themselves with mydisclosure.

All the remote control stations so far described were provided withindividual warning lights and two control switches; one for indicating,by illumination of the warning lights, to all other remote controlstations that the machine was engaged, and a second one in the form of afoot pedal or hand switch to start and stop actual operation of themachine. It will be understood, that for certain purposes remotestations of a much simpler construction may sufifice which have nowarning light and only one control switch. Two such simplified stationsare shown in Figure 4, each com-prising merely a microphone I38connected across leads I35 and I35 of a D. C. communication circuit, anda foot pedal or hand switch II2 adapted to close the D. C. circuit fortransmission of audio messages to the recording machine. Closing of footpedal switch I72 will at the same time cause operation of the motor. Asystem using exclusively remote control stations of this type requiresonly one relay coil in the master station to close the power circuit ofthe motor upon the closing of foot pedal switch I12.

A simplified system of this type is particularly appropriate in caseswhere one and the same person may wish to dictate notes from apluralassociated with said microphone means for regr iaia 9 ity" ordifierent rooms with no likelihood of another person using the samemachine, such as in a doctors office having several examination rooms.In a practical embodiment of my invention constructed according to thediagram of Figure l are employed the following circuit constants:

Contact 13 110 volt power line Stepdown transformer 20: 1 Primary 21 110v. A. 0,

Secondary 22 ;L 18 v. A. C. 10 Audio transformer 31:

Primary 32 100 ohms impedance Secondary 33 100,000 ohms impedance'Stepdown transformer 50:

Primary 51 110 V. A. O.

' 10 v. A. C. Audio transformer 80 15 Primary 81. 10,000 ohms impedance100 ohms impedance 2.3 henrics, 65 ohms D. G.

resistance Secondary 8 Choke coil 26.--

Relay 60 35 milliwatts Relay 65 5 milliwatts Rectifier 23, seleniumrectifier." 12-14 v. D. 2A. 8v. D. 0.3A. -2() Condenser 2S Condenser 2940 mi. 40 mi.

Resistor 84 5000 ohms 25 Potentiometer S3. 15,000 ohms Lamps 56, 56 6-8V., ,15 A.

ulating the current flow in saidcommunication circuit and a visualsignalling device having a normally interrupted power supply circuit;said first relay being adapted to close the power supply circuit forsaid signallin device in response 0 to current fiow in saidcommunication circuit and said second relay being adapted to close thepower supply circuit for said motor in response to a predeterminedincrease in said current flow over that required to activate said firstrelay.

2. An arrangement for recording sound from a plurality of remote pointsincluding a centrally positioned recording machine having an electronicamplifier, a motor and a normally open power'supply circuit therefor; acommunication circuit inductively coupled to said amplifier andcomprising a source of D. C. voltage, a first relay, a second relayrequiring a. stronger current fiow for activation than said first relayand a plurality of remotely positioned resistance type microphonesconnected in series with said relays but parallel to one another; andassociated with each microphone means for regulating the current flow insaid communication circuit and a visual signalling device having anormally interrupted power supply system common to the signallingdevices associated with all of the other microphones; said first relaybeing adapted to close the power supply system of said signallingdevices in response to current flow in said communication circuit, andsaid second relay being adapted to close the power supply circuit forsaid motor-in response'to a predetermined increase in said current flowover that required to activate said first relay.

3. Arrangement for remote control operation of a recording machine ofthe type having an,

electronic amplifier, a motor and a normally interrupted power supplycircuit therefor; said arrangement including a communication circuithaving a source of D. C. voltage, a first relay, a second relayrequiring stronger current flow in said circuit for actuation than saidfirst relay, a winding forming part of an audio transformer operativelyconnected to said amplifier, a remotely positioned resistance typemicrophone and associated therewith a resistor, a, first switch adaptedto close said communication circuit through said resistor, a secondswitch adapted to -by-pass said resistor, and a visual signalling devicehavin a normally interrupted power supply system, said first relay beingarranged, upon closing of said first switch, to close said power supplysystem for said signalling device, and said second relay being arranged,upon closing of said second switch, to close said. power supply circuitfor said motor.

4(Arrangement for remote control operation of a recording machine of thetype having an electronic amplifier, a drive system and a normallyinterrupted control circuit therefor; said arrangement including acommunication circuit, having a source of D. C. voltage, a first relay,a second relay requiring stronger current fiow in said circuit foractuation than said first relay, a winding forming part of an audiotransformer operatively connected to said amplifier, a plurality ofremotely positioned resistance type microphones connected in series withsaid relays and said winding but in parallel to one another, andassociated with each microphone a resistor, a first switch adapted toclose said communication circuit through said resistor, a second switchadapted to by-pass said resistor; and signalling means associated withsaid microphones respectively and having a common, normally interruptedpower supply system, said first relay being adapted, upon closing of anyone of said first switches, to close said power supply system for allsaid signalling means independently of activation of said second relay,and said second relay being adapted, upon closing of any one of said*second switches, to close said control circuit for said drive system.

5; An arrangement for recording sound from a remote point, including arecording machine having an electronic amplifier, a power circuit toheat said amplifier, a, drive system and a normally interrupted controlcircuit effective when closed to render said drive system operative; acommunication circuit inductively coupled to said amplifier andincluding a relay, a plurality of remotely positioned resistancetypemicrophones in series with said relay and parallel to one another and amanually operable switch associated with each of said microphones toclose said communication circuit for operation, a power supply circuitincluding a rectifier adapted to supply said communication circuit withdirect current; and common to all said power supply circuits a source ofpower and a master control switch adapted to connect said source ofpower simultaneously into said power circuits, said relay being arrangedto close said normally interrupted cosm c ma ly in err p d power i ittor contr lli said-drive system; a communication circuit indu ti lv c ul to s am lifie n i c udin a number of relays'responsive to'D. 'C.currents 01- different magnitudes," a remotely positioned r s st nc eicro e owe su l ir- Quit in l i a c i e a pt d o sim l sa d com nic tciicuit th d ect curren and associated with said microphone means iorcontrolling the flow of D. C. current in said cornmunication circuit; asignalling system including a source of light in proximity of saidmicrophone, a normally interrupted power supply circuit to energize saidsignalling system; and common to all said power supply circuits a sourceof power and a master control switch adapted to connect Sa d so rc ofpowe simultaneously i to a l aid power circuits, said relays beingarranged to close idnc m fly rru d DQ Q 'QiE iii in p se t d cc c r cnflq i i said comm nication circuit.

'7. An arrangement for recording scund from a number of remote pointsincluding a recording ma hin ha n e e troni amp ifies a new r c r t t asa pl e a m o and. a normally interrupted power circuit to drive saidmotor; a c mmunica n rcui iidiw i lv l t d am fi nd' i ud ne a umbe ofre ys r p si e D.- C- curre t 0i ffi ifeiii magnitudes, a plurality of.remotely positioned parallel-connected carbon microphones, a powersupply circuit including a rectifier adapted to supply saidcommunication circuit with direct current and, associated with eachmicrophone means for controlling the now of D, C, current in saidcommunication circuit; a signalling syst r nc udi a mora y f se ies. ned lam s o e a h s c ated. w th, ever 1 9 10.,- phone, a normallyinterrupted power supply circuit for energization of said signallingsystem; nd common to l, aid w is ipp y cir it 3 source of power and amaster control switch adapted to connect said sourceoi power, sim'ultaneously into allsaid power circuits, said relays being arrangedtoclose said normallyinterrupted power supply circuits in response todirect curl flo in a d c mmi iii i ori W 1 a a ow irs i i e ivi ie ri v temsof the type described, a rectifier having out; put terminals, incombination with a filter arrangement connected, across said terminals,saidfilter arrangement including a choke coil and a number ofrelay'coils connected in series'with said choke coil at'the' lowpotential end thereof and, a number of condensers connected across saidterminals at the low potential ends of said choke'coil and said relay"coils.

9. In an arrangement for remote control operation of a recordin machineof the type having a recorder, a drive system and a control circuitforputting said drive system into and out of operation: the combinationof a communication circuit serially includin a source of direct current,a remotely positionedresistance type micro phone, a primary windingforming part of an audio transformer, a, relay oil having an associatedpair of contacts, and a manual switch adjacent to said microphone forclosing said com munication circuit to cause direct current to flowtherein; means connecting said relay con-'- tacts in said controlcircuit to cause the latter to be closed to render said drive systemoperative upon closing of said manual switch; a secondary windingincluded in said audio transformer; cir- Qui means. conn ct n sa d ecndar wind n t sa d e o e o sup l th re o u io. module,- oiits imposed onth d r u r i said s me munication circuit by said microphone; and asound condenser in said communication circuit forming a by-pass for theaudio currents around said relay coil and D.-C. source.

10. The combination set forth in claim 9 wherein said source of directcurrent comprises a rectifier and a filter, said filter comprising saidrelay coil acting as a choke.

11. In an arrangement for remote control operation of a recordingmachine of the typefhaving a recorder, a drive system and a controlcircuit for putting said drive'system into. and out of operation: thecombination of a communication circuit serially including a source" ordirect cur:- rent, a remotely positioned resistance type microphone, aprimary winding forming part or an audio transformer operativelyconnected to said recorder, a first relay, a second relay requiring astronger current fiow in said communication circuit for activation thansaid first relay, and a first switch adjacent to said microphone for.cl'os ing said communication circui t to cause direct current flowtherein and activation of said relay; a signaling device controlled bysaid. first relay to render 'it operative when the'relay is activated;means associated with said communi cation circuit and including a secondswitch adjacent to said microphone and operable to: increase the currentflow in said communication circuit to cause activation of said secondrelay; and means connecting said second relay to said: con trol circuitto placesaid drive system in operation when said second switch isoperated.

' 12. In an arrangementincluding a dictation recording machine havinga'reccrder and a drive system and including a remote stationiorf con:trolling said machine: the combinationof a can munication circuitleading'from said station'to said machine and including a source ordirect current, a resistance type microphone, a resistor and a'firstswitch closable to cause flow of direct current in said circuit; a firstcontrol device for said machine connected in said'communicatiofi circuitand activatable by the direct current therein when said first switch isclosed; a n'o'rmally-open second switch connected in shunt with saidresistor for shorting the latter to cause an increase in now of directcurrent in saidcoin' munication circuit; a second control device forsaid machine. connected insaid communication circuit fol-activation bythe direct current therein, saidsecond control device requiring a highervalueiof direct current for activation than said first controldeviceandbeing activated only when both said first. and second switches areclosed, said microphone being operable to modulate the direct current insaid"communicatiori'circuit when both said first and said secondswitchesare closed; "and means for feeding audio modulations insaidconimunication circuit tosaid recorder."

e r RIcHARn oBnEr-t REEZQBENCES CITED The following references are ofreco rd in,tne

file r this patent:

' U irEa r r TEus au s ee- -9 3

